1. Field of the Invention
This invention relates generally to communication systems, and, more particularly, to heterogeneous communication systems.
2. Description of the Related Art
A conventional communication system uses one or more access nodes to provide network connectivity to one or more mobile nodes. For example, in a cellular communication system that operates according to Universal Mobile Telecommunication Services (UMTS) standards, one or more nodes may be used to provide wireless network connectivity to mobile nodes. The access networks may include wireless access nodes such as base stations, base station routers, access points and the like, which may be connected to a communication network by radio network controllers. The mobile nodes may include cellular telephones, personal data assistants, smart phones, text messaging devices, Global Positioning Systems, navigation systems, network interface cards, notebook computers, desktop computers, and the like. For another example, an access network that operates according to IEEE 802.3 standards may also be used to provide wired network connectivity to a mobile node that has a wired connection to an access node in the wired access network.
Numerous types of communication systems have been developed and deployed to provide network connectivity to mobile nodes. Exemplary communication systems include wire-line communication systems, such as Internets, intranets, systems that operate according to IEEE 802.3 standards, and the like. Wireless communication systems have also proliferated. Exemplary wireless communication systems include systems that provide wireless connectivity to micro cells (e.g., systems that provide wireless connectivity according to the IEEE 802.11 or IEEE 802.15 standards) and systems that provide wireless connectivity to macro cells (e.g., systems that operate according to the Third Generation Partnership Project standards—3GPP, 3GPP2—and/or systems operate according to the IEEE 802.16 and IEEE 802.20 standards).
The coverage provided by these heterogeneous communication systems may intersect and/or overlap. For example, a wireless access point for a wireless local area network may provide network connectivity to mobile nodes in a micro cell associated with a coffee shop that is within the macro cell coverage area associated with a base station of a cellular communication system. For another example, a wire-line connection may be available in an office building that also provides network connectivity via a wireless local area network. The office building may also be in a geographic area that receives cellular telephone coverage from one or more service providers.
At least partly in response to the proliferation of different communication systems, mobile nodes that support more than one type of access network have been developed. For example, a smart phone may support a wireless communication interface for accessing networks over an air interface and a wire-line communication interface for accessing networks when a physical connection to an access node is available. Mobile nodes that support multiple communication interfaces may hand off from one access node to another. Handoffs are typically triggered by one or more metrics such as signal quality, synchronization time differences, transmission error rates, access node loading conditions, and the like. For example, a moving mobile mode may encounter regions where the signal quality provided by one access node drops and may therefore handover to another access node having better signal quality. For another example, the signal quality provided to a stationary mobile node by a first access node may vary due to changing environmental conditions, triggering a handoff to a second access node.
Smooth handoffs between access nodes that operate according to different communication technologies, standards, and/or protocols may be difficult (or impossible) because of differences or incompatibilities between the different access nodes. The IEEE 802.21 standard has therefore been proposed to enhance the user's experience in mobile networks by supporting handovers between access nodes of heterogeneous networks. In particular, the IEEE 802.21 standard, which is also referred to in the art as the Media Independent Handover (MIH) standard, defines a specification that provides link layer intelligence and other related network information to upper layers to optimize handovers between heterogeneous media. This includes links specified by 3GPP, 3GPP2 and both wired and wireless media in the IEEE 802 family of specifications.
The MIH 802.21 protocol defines event services, command services, and information services. The Media Independent Information Service (MIIS) provides a framework and corresponding mechanisms by which a MIHF (Media Independent Handover Function) entity may discover and obtain network information existing within a geographical area to facilitate the handovers. The command service enables higher layers to control the physical, data link, and logical link layers (also known as “lower layers”). The higher layers may also control the reconfiguration or selection of an appropriate link through a set of handover commands. Event services are used to transmit information regarding events between access nodes and mobile nodes. Events may indicate changes in state and/or transmission behavior of the physical, data link and logical link layers, or predict state changes of these layers. The event service may also be used to indicate management actions or command status on part of a network or some such management entity.
Access nodes and/or mobile nodes may request that certain events be reported using an event registration or subscription message. For example, a mobile node may use remote event services to learn about network events, such as its loading condition, scheduled maintenance, and unavailability. Similarly, the network can learn about various conditions observed by the mobile node, such as channel conditions, signal strength or BER, by requesting that the mobile node transmit this information as events. Radio conditions can change very frequently, which may trigger frequent reporting of events resulting from these changes. Event registration may reduce the number and/or frequency of event reports by registering for events that are of interest to the node and also by conveying a threshold value associated with the requested event. The requested events are only reported when the threshold set by the requesting node is exceeded.
In a conventional heterogeneous network, mobile nodes initiate network discovery, and then notifies the network of the existence of the mobile node. Once network discovery has taken place, the network may request that certain events be reported, e.g., using an event registration message that may be initiated by the network. The mobile node may provide confirmation of the event registration in response to the event registration message. Similarly, the mobile node may initiate event registration, e.g., using an event registration message, if the mobile node wants to receive events from the network. The network and the mobile node may then form and store event context information based on the information included in the event registration message(s). However, transmission and acknowledgment of the event registration messages increases the overhead associated with implementing media independent handovers.